It is known that, in order to effect such an analysis, use is generally made of a sampling apparatus for depositing microorganisms, such as bacteria, yeasts, or moulds, present in an air sample, on a layer of growth media in a receptacle, and that next this receptacle is put to incubate at the required temperature and for the required length of time to enable the deposited micro-organisms to develop in the form of colonies visible to the naked eye, so that they can be counted and identified.